The present invention relates to chilling poultry and, more particularly, to the chilling of chicken such that prolonged shelf life may be obtained.
In order to meet a continuing retail demand for fresh, as opposed to frozen poultry, it is necessary to eviscerate and dress poultry such as chicken and to maintain the same at suitable temperatures prior to retail sale. Typically, dressed chicken is chilled to and maintained at a temperature of 32.degree.-35.degree. F. at which growth of bacteria (i.e. spoilage) is strongly retarded. In this manner, chicken is preserved in a `fresh` condition as it is transported, distributed and placed on shelves for retail sale. Clearly, the longest shelf life which can be readily obtaned is desired to avoid lost sales due to spoilage of the poultry product.
In a typical poultry processing plant, chickens are prepared for shipment by chilling to a temperature of 32.degree.-35.degree. F., generally in an ice water bath. It is common practice in dressing chickens to automatically remove parts comprising the giblets, eviscerate the carcass and reinsert the giblets. In fact, in large chicken processing plants, economics dictate that virtually all such operations be automated and equipment for so automating chicken processing is commercially available.
It is also common practice to package dressed chickens for shipment by placing a dozen or so chilled chickens in a carton and then cover such chickens with water ice before sealing the carton. The use of water ice adds to the net weight of shipped poultry and thereby increases transport costs as well as resulting in the inconvenience of handling cartons which inevitably become wet with melted water ice. It is also known to pack dressed poultry with dry ice (solid carbon dioxide) and although the problems of melting water ice are avoided, dry ice is more costly and still adds to the net weight and hence cost of shipping the poultry product. Charges of dry ice may be injected into poultry carcasses as described in U.S. Pat. No. 3,932,155, which is assigned to the assignee of the present invention, but these techniques have resulted in damage to the carcasses due to the high CO.sub.2 injection pressures utilized.
In order to avoid the aforementioned problems of maintaining poultry in a chilled condition, it has been proposed to insert chilled poultry in gas flushed bags and simply ship such bags in standard cartons. In this packaging process, a vacuum withdraws ambient atmosphere from the bags prior to introducing an inert gas such as carbon dioxide. The chilled poultry, say 10-12 chickens, is then placed in the bag which is typically comprised of a plastic material. The bags are heat sealed to retain the inert atmosphere (CO.sub.2) therein and shelf lives of 20-22 days have been obtained for poultry so packaged.
It has been found that poultry such as chicken chilled or refrigerated in cartons packed with dry or water ice, or chickens placed in gas flushed bags, tend initially to develop the evidence of spoilage internally of the carcass, i.e. the walls of the breast cavity. The above mentioned chilling techniques, with the exception of the process described in U.S. Pat. No. 3,932,155, do not result in the introduction of any significant quantities of refrigerant internally of the poultry carcass and relatively short, say 10-22 day shelf life results. Although the process described in the above mentioned U.S. Patent enables introduction of CO.sub.2 snow internally of poultry carcasses, such techniques cause a discharge of snow at pressures which frequently physically damage the poultry being chilled. Also, as carbon dioxide snow exhibits a temperature of -109.degree. F., the interior portions of poultry are frozen by use of the process described in this patent.
During the transport of poultry packaged by any of the techniques described above, the desired temperature of a trailer is established and typically maintained by a mechanical refrigeration unit. In the past, there has been a tendency to operate trailer refrigeration units at temperatures so that the average temperature of transported poultry is not just maintained but is actually reduced to a satisfactory level. However, there have been instances in which trailer refrigeration systems have not been adequate to effect such temperature reductions and loads of dressed poultry have been `rejected` at their destination for failure to arrive at or below a prescribed maximum temperature.
Accordingly, a clear need exists for an effective poultry chilling process which enables increased shelf life to be obtained without the inconvenience associated with water ice chilling techniques and which is compatible with automated poultry processing lines.